1. Field of the Invention
The present invention relates to a cable checker and more particularly pertains to a cable checker employing logic circuitry whereby the two ends of a cable may be plugged into the checker so as to drive one or the other of a pair of light emitting diodes which respectively indicate the proper or improper functioning of the cable.
2. Description of the Prior Art
With respect to devices utilizable to test for faults, such as short circuits or the like, in electrical cables, there have been a number of such devices constructed which are typically large and bulky in size, as well as complex in construction and expensive to manufacture. For example, U.S. Pat. No. 2,810,881, issued to Daily on Oct. 22, 1957, illustrates a typical prior art automatic cable tester which requires a 120 volt power supply and which employs 55 components, as well as 19 mechanical relays, switches, and potentiometers. The device further includes a pair of sockets to which the ends of a cable may be connected as well as 27 different lights to indicate both circuit operation and cable functioning.
Another cable tester which is operable to locate short and open circuits in wires is to be found in U.S. Pat. No. 2,862,179, issued to Murphy on Nov. 25, 1958, such tester employing two terminals to which a cable may be attached for test purposes. In this respect, the Murphy device is illustrative of the earlier prior art testers which made no use of logic circuitry, as with the above-mentioned Daily device, and which employed the use of meter movements, as well as a plurality of switches, to effectively test a cable. Similarly, U.S. Pat. No. 3,131,347, issued to Brooks et al on Apr. 28, 1964, illustrates a cable testing system for detecting open and short circuits which employs 15 different mechanical parts and 59 various electrical components, and further includes a 120 volt power supply and time delayed operation introduced by the mechanical closure of relays. By the same token, another prior art cable tester is to be found in U.S. Pat. No. 3,480,856, issued to Scott on Nov. 25, 1969, such tester also requiring a 120 volt power supply and utilizing 26 different components including switches and electron tubes. As with all of the aforementioned cable testers, the device of Scott is bulky in size and lacks portability and simplicity in construction.
At least one cable tester has been designed which is somewhat portable in construction and which employs some logic circuitry in its design. In this respect, U.S. Pat. No. 3,986,106, issued to Shuck et al on Oct. 12, 1976, illustrates a portable cable test set which includes a master unit connected to one end of a cable made up of multiple wire pairs and a remote unit connected to the other end of the cable. The master unit generates a series of digital pulses whereby one pulse is applied to a first wire of each wire pair in a predetermined sequence. The remote unit interconnects the wire pair with a resistor of predetermined resistance which differs from every other resistor and which is much greater than the resistance of the wire pair undergoing testing. A corresponding resistor of like value is included in the master unit and receives the same pulse as applied to the wire undergoing testing. A comparator in the master unit compares the magnitude of the pulse sent over the wire pair with the magnitude of the pulse sent through the reference resistance in the master unit, and a sequencer applies the next pulse to the next wire and corresponding resistance when the preceding pulse magnitudes are equivalent. An interrupting stops the test sequence when the compared pulses are unequal in magnitude, and an indicator then identifies the wire pair having conditions activating the sequence interrupter. While the Shuck et al tester is modern in construction and effective in its operation, a large number of electronic components are required to construct the tester thus limiting its compactness and portability, as well as its ease of manufacture. Further, as can be appreciated, the Shuck et al tester is quite expensive to construct due to the large number of electronic components contained therein and as such, there still exists an ongoing need for simpler and more economically constructed cable testers which are compact in size and which are highly reliable in their operation. In this regard, the present invention fulfills this need.